The enhancement-mode metal-oxide-semiconductor field effect transistor (EMOSFET) is one of the most widely used devices in the design of metal-oxide semiconductor (MOS) integrated circuits. Silicon complementary MOS (CMOS) technology is a mature technology for EMOSFET design, offering simplicity in design and low power consumption. However, Group III-V compound semiconductor technology continues to serve as an attractive technology for EMOSFET design due to its superior speed/power performance and efficiency.
One class of EMOSFETs is designed with self-aligned ion implants to form low resistivity source and drain extensions. However, manufacturing III-V compound semiconductor EMOSFETs with ion implanted source and drain extensions is difficult. The implant material can act as both a donor or an acceptor depending on its association with either the Group III or the Group V site in the lattice, respectively. Further, annealing temperatures used to form the source and drain extensions, typically higher than 700° C. in n-channel devices, may be incompatible with the semiconductor/gate oxide interface stability. The ion implantation process used to form the source and drain extension also may result in an undesirably high trap density at the semiconductor/gate oxide interface. Moreover, formation of the source and drain extensions requires in most technologies that the gate electrode be used as a mask and thus be formed before ion implantation, therefore limiting manufacturing flexibility. Further, the source and drain extensions of such devices typically have sheet resistances of greater than 300 to 400 ohms/square when annealed at temperatures of about 800° C. and above, and of greater than about 500 ohms/square when annealed at temperatures of about 700° C.
Accordingly, a need exists for an “implant-free” III-V compound semiconductor EMOSFET. As used herein, the term “implant-free” shall mean free from source and drain extensions formed by ion implantation. A need also exists for a method for fabricating an implant-free enhancement mode metal-oxide-semiconductor field effect transistor. Other desirable features and characteristics of the present invention will become apparent from the subsequent description and the appended claims, taken in conjunction with the accompanying drawings.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.